This work consists of three projects which explore the effects of exercise, airway geometry, and to a limited extent, selected pulmonary diseases upon the measurement of inert gas bolus-response using a previously developed experimental technique. The measurement will consist of monitoring both the inspired and the expired concentration-volume curves generated by a 20 ml bolus of helium or sulfur hexafluoride which is automatically introduced into inspired air. From this data the extent of airway mixing and alveolar ventilation by inert gas will be computed. In Project I, a sequence of bolus-response measurement will be made during exercise. The resulting values for extent of mixing and alveolar ventilation will be correlated with heart rate in order to determine the influence of cardiogenic mixing mechanisms. In Project II, the effects of airway branch points, transport path asymmetries, and upper airway geometry will be investigated in plastic models. The extent of mixing will be determined from bolus-response measurements between the upstream and downstream sampling sites of the models and this data will be correlated using a previously developed tubular mixing theory. In Project III, a preliminary evaluation of the effect of pulmonary disease upon bolus-response will be performed. The bolus-response measurements from a group of 10 patients with defined disease (emphysema, bronchitis, small airway disease, asthma) will be compared to those of normal subjects. In addition the fundamental information regarding airway mixing, this project will provide the opportunity to develop a prototype clinidal apparatus and to assess the utility of the non-invasive bolus-response measurements as a test of pulmonary dysfunction.